1. Field of the Invention
This invention relates to an improved method of dehydrating ketone dewaxing solvent. More particularly, this invention relates to an improved method of dehydrating ketone dewaxing solvent wherein the improvement resides in eliminating a reboiler on the ketone dehydrating tower. Still more particularly, this invention relates to an improved method of dehydrating ketone dewaxing solvent recovered from dewaxed oil and a wax slurry via flash vaporization followed by steam stripping, whereby water is removed from the recovered solvent via the use of a decanting drum, a deketonizer tower, and a dehydration tower, the improvement comprising passing at least a portion of the hot overhead vapors from the wax flash vaporization directly to the bottom of the dehydrator thereby eliminating the need for a reboiler on the dehydrator.
2. Description of the Prior Art
The use of ketone solvents for dewaxing waxy petroleum oils is well known in the art. Solvents employed in ketone dewaxing processes are generally ketones containing from 3 to 6 carbon atoms such as acetone, methylethyl ketone, methylisobutyl ketone, etc., and mixtures thereof. The ketone solvents may also be admixed with aromatic solvents such as toluene, xylene, benzene, petroleum naphthas or mixtures thereof.
Solvent recovery is an integral part of any solvent dewaxing process, since the dewaxing solvent must be removed from both the dewaxed oil and wax and recycled back into the dewaxing operation. Most of the dewaxing solvent is removed from the oil and wax via flash evaporation, or simple distillation. However, small quantities of solvent remain in both the oil and wax even after distillation or flash evaporation. These small quantities of solvent are generally removed via a stripping operation wherein a gas such as nitrogen, a low molecular weight hydrocarbon or steam is passed through the wax and oil carrying with it any solvent that remained therein after distillation. Steam stripping is convenient and economical to use, but it introduces water into the solvent which must then be removed.
Typical of a ketone dewaxing and solvent recovery process which includes steam stripping and subsequent dehydration of the recovered solvent is that disclosed in U.S. Pat. No. 3,105,809. In this process, the bulk of the ketone dewaxing solvent is removed from both the dewaxed oil and wax slurry via distillation with the small quantities of solvent remaining after distillation removed from the oil and wax via steam stripping. The wet solvent overheads from the steam strippers are then condensed and passed to a decanting or solvent setting drum. In the decanting or solvent settling drum, the condensed liquid from the stripper overheads settles into a heavy, water-rich phase saturated with solvent and a light, solvent-rich phase which is saturated with water. The water-rich phase or liquid is drawn off from the bottom of the drum and steam distilled in a deketonizing tower. The steam removes the solvent from the water with the resulting solvent-free water then passed to a sewer and the solvent-containing overheads are returned to the solvent settling drum. The solvent-rich upper layer in the drum is fed as reflux to a simple distillation tower or solvent dehydrator provided with a reboiler. A portion of the condensed solvent from the oil and wax solvent recovery vaporization is also fed to the dehydrator. The overhead consisting of water and solvent is condensed and returned to the decanter drum while essentially water-free solvent is drawn off the bottom of the tower and recycled back to the dewaxing operation.